1. Field of the Invention
The present invention relates to a fluid filter and a method of using the fluid filter, and more particularly to a fluid filter having a simple, reasonably-priced structure and a method of using the fluid filter, with which the sealing property of a drainage path can be secured over a long period of normal use and the operability of a fluid drain can be improved during element replacement.
2. Description of the Related Art
In a known conventional oil filter, a filter element is accommodated in a substantially vertical casing constituted by a case and a cap which can be engaged with each other by relative rotation, and when the cap is loosened from the case during element replacement, oil is drained internally from a drainage path provided in the case (see Patent Document 1 and Patent Document 2, for example).
Patent Document 1 discloses a device in which a discharge path 19 (drainage path) formed in the case is provided with an axially movable valve body 5 and a spring 20 which biases the valve body 5 upward. When the cap is fastened to the case, the valve body 5 is pushed downward by an end plate 37 provided on an axial end surface of an element 4, thereby sealing the discharge path 19. On the other hand, when the cap is loosened from the case, the valve body 5 is moved upward by the action of the spring 20 such that the discharge path 19 is opened (see FIG. 2 and so on of Patent Document 1).
Patent Document 2 discloses a device in which a downwardly projecting projection 12 is provided on the bottom surface of a resin case 11 holding an element 8, and a bypass oil path 6 (drainage path) formed in a base 2 is opened and closed by inserting and removing the projection 12 into and out of the bypass oil path 6 (see FIGS. 1, 2, and so on, and the first embodiment of Patent Document 2).
Patent Document 2 also discloses a device in which two O-rings 53 and 54 are provided in a groove portion on the bottom surface of a resin case 51 holding the element 8, and the bypass oil path 6 (drainage path) formed in the base 2 is opened and closed by pressing and separating these O-rings 53 and 54 so as to surround the bypass oil path 6 (see FIG. 3 and so on, and the second embodiment of Patent Document 2).
Patent Document 2 also discloses a device in which a check valve 39 is provided on the bottom surface of a resin case 31 holding the element 8, and the bypass oil path 6 (drainage path) formed in the base 2 is opened and closed by pressing and separating the check valve 39 against and from the bypass oil path 6 (see FIGS. 4, 5, and so on, and the third embodiment of Patent Document 2).
However, in Patent Document 1, the spring 20 is provided for biasing the valve body 5 upward, and therefore the spring 20 must be pushed by the element 4 when the cap is fastened to the case, causing an increase in the fastening load. Moreover, the opening/closing mechanism constituted by the valve body 5 and the spring 20 is provided on the case side, leading to an increase in the number of components and creating a structure which is complicated and expensive. Furthermore, the end plate 37 must be provided for pushing the valve body 5 against the axial end plate of the element 4.
In the first embodiment of Patent Document 2, the projection 12 is inserted into and removed from the drainage path, and hence the projection 12 must be guided toward and inserted into the opening in the drainage path manually by an operator when the cap 1 is fastened to the base 2, and this insertion operation is complicated. Also, oil drainage is begun by loosening the cap 1 from the base 2 such that the engagement therebetween is completely released, and then raising the cap to remove the projection 12 from the drainage path. As a result, oil drainage begins after the engagement between the case and the cap has been released, which may lead to oil spillage and so on.
In the second and third embodiments of Patent Document 2, a sealing member (the O-rings 53 and 54 and the check valve 39) is pressed against the surface of the base 2 to seal the drainage path, but when the cap 1 is fastened to the base 2, the element 4 is turned together with the cap 1 such that the sealing member slides over the surface of the case. This creates wear on the sealing member, making it impossible to secure a drainage path sealing property over a long period of normal use.
Moreover, in the first through third embodiments of Patent Document 2, the protrusion 12, O-rings 53 and 54, and check valve 39 are provided on the element side, and hence the case 11, 51, 31 for holding the element must be provided.
Patent Document 1: Japanese Patent Application Publication No. JP-A-11-137917
Patent Document 2: Japanese Patent Application Publication No. JP-A-11-33313